> If everyone refused to build guidance systems for missiles, perhaps the missiles would never get built?

Correct but incomplete.

In that scenario, unguided rockets get built instead of missiles. Rockets, being unguided, will miss their targets more often than missiles. Rockets, being unguided, will also tend to be used in slightly-scattered volleys, so as to increase the chance that at least one rocket hits the target.

Any explosive ordnance that misses its target has some chance of instead killing some civilians.

Do you see the problem here?